"Why waste money or time on human actors when most customers just want explosions?"

Indeed! Watch any Roland Emmerich film and you will see the absolute last word in such stupidity.

However, I don't think it's because the public started out stupid. Hardly! Rather, they have been taught to become stupid by an industry that would rather feed them predictable garbage than bother offering them better fare. People slowly become brutalized by being offered a steady diet of brutality, and then they want more of it, and they don't know why. It becomes a self-replicating thing, and that's what the marketers want...just like they want us to become addicted to all the other moronic stuff they sell.